Preparation of bead-form expandable styrene polymers

Abstract

Bead-form expandable styrene polymers are obtained by suspension polymerization of styrene with addition of from 1 to 10% by weight of C 3 - to C 7 -hydrocarbons and/or carbon dioxide as blowing agent and, if desired, conventional additives, using, as suspension stabilizer, a mixture of magnesium pyrophosphate, a sulfonate group-containing extender and an alkali metal carboxylate or alkaline earth metal carboxylate, the magnesium pyrophosphate being prepared immediately before the polymerization by combining an aqueous solution of alkali metal pyrophosphate with at least the stoichiometrically necessary amount of a magnesium salt.

We claim: 
     
       1. A process for the preparation of bead-form, expandable styrene polymers by polymerizing styrene, in the presence or absence of further comonomers, in aqueous suspension in the presence of suspension stabilizers and conventional styrene-soluble polymerization catalysts and with addition of from 1 to 10% by weight of a C 3  - to C 7  -hydrocarbon and/or carbon dioxide as blowing agent and, optionally, conventional additives in effective amounts, which comprises using, as suspension stabilizer, a mixture of magnesium pyrophosphate, a sulfonate group-containing extender and an alkali metal or alkaline earth metal carboxylate, the magnesium pyrophosphate being prepared immediately before the polymerization by combining an aqueous solution of an alkali metal pyrophosphate with at least the stoichiometrically necessary amount of a magnesium salt. 
     
     
       2. A process as claimed in claim 1, wherein magnesium pyrophosphate is employed in a concentration of from 0.03 to 2.0% by weight, based on the aqueous phase. 
     
     
       3. A process as claimed in claim 1, wherein the extender employed is an alkali metal salt of a mixture of C 12  -C 17  -alkylsulfonic acids. 
     
     
       4. A process as claimed in claim 1, wherein the extender employed is an alkali metal salt of dodecylbenzenesulfonic acid. 
     
     
       5. A process as claimed in claim 1, wherein a carboxylate containing at least one olefinic double bond is employed. 
     
     
       6. A process as claimed in claim 5, wherein an acrylate is employed. 
     
     
       7. A process as claimed in claim 1, wherein the alkali metal pyrophosphate used is Na 4  P 2  O 7  and the magnesium salt used is MgSO 4  ·7H 2  O.